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Abstract

We demonstrate a new kind of optical spectrometer employing photonic crystal patterns to outcouple waveguided light from a transparent substrate. This spectrometer consists of an array of photonic crystal patterns, nanofabricated in a polymer on a glass substrate, combined with a camera. The camera captures an image of the light outcoupled from the patterned substrate; the array of patterns produces a spatially resolved map of intensities for different wavelength bands. The intensity map of the image is converted into a spectrum using the photonic crystal pattern response functions. We present a proof of concept by characterizing a white LED with our photonic crystal spectrometer.

Figures (6)

Illustration of spatially resolved, wavelength-selective outcoupling of waveguided light using and array of photonic crystals. Light waveguided into the edge of the substrate is outcoupled by photonic crystal patterns corresponding to different bands of wavelengths.

Scattering of three guided modes with |k∥| = √kx2 + ky2 = k1 (solid blue), k2 (solid green), and k3 (solid red) by a reciprocal lattice vector G into |k1 + G| (dashed blue), |k2 + G| (dashed green), and |k3 + G| (dashed red). Modes scattered (i) outside of the dashed gray circle (|k∥| > nk0) are evanescent in the slab, (ii) into the annulus bounded by the dashed gray and solid gray circles (nk0 > |k∥| > k0) are guided in the slab and evanescent in air, (iii) into the annulus bounded by the solid gray and black circles (k0 > |k∥| > NAk0) propagate in air but cannot be imaged by the camera, and (iv) inside the solid black circle (|k∥| < NAk0) propagate in the air and can be imaged by the camera.

Response of a 3×3 array of photonic crystal patterns to different inputs. (a) 470nm waveguided light is primarily outcoupled by two array elements in the bottom row, (b) 530nm waveguided light is primarily outcoupled by two array elements in the middle row and one in the bottom row, (c) 630nm waveguided light is primarily outcoupled by two array elements in the top row, and (d) a white light emitting diode (LED) spectrum is outcoupled by array elements in all rows. Each photonic crystal array element measures approximately 30μm × 30μm; the total array size is approximately 100μm × 100μm .

Comparison of photonic crystal spectrometer and commercial spectrometer. Comparison of white LED spectrum measurement using commercially available spectrometer, calculated spectrum projected on to the pattern spectral response function basis shown in Fig. 4, and measurement using the photonic crystal spectrometer.